Chemical Reactions Vocabulary Synthesis Decomposition Single replacement Double

Chemical Reactions Vocabulary Synthesis Decomposition Single replacement Double replacement Combustion Net Ionic equation Solid Precipitate Net Ionic Equation Half Rxn REDOX Rxn Oxidation Reduction

Objectives: 1. Classify types of chemical reactions. 2. Predict products of reactions using the provided charts. 3. Write a net ionic equation. 4. Explain and deconstruct REDOX reactions.

Review (LAST THING WE DID BEFORE BREAK!)

Chemical Reactions • The process by which one or more substances are rearranged to form different substances is called a chemical reaction. • Evidence of a chemical reaction – Change in temperature – Change in color – Odor, gas, or bubbles may form.

Chemical Reactions • Chemists use statements called equations to represent chemical reactions. • Reactants are the starting substances. • Products are the substances formed in the reaction. • This table summarizes the symbols used in chemical equations.

Representing Chemical Reactions (cont. ) • In word equations, aluminum(s) + bromine(l) → aluminum bromide(s) reads as “aluminum and bromine react to produce aluminum bromide”. • Skeleton equations use symbols and formulas to represent the reactants and products. Al(s) + Br(l) → Al. Br 3(s) • Skeleton equations lack information about how many atoms are involved in the reaction.

Representing Chemical Reactions (cont. ) • A chemical equation is a statement that uses chemical formulas to show the identities and relative amounts of the substances involved in a chemical reaction.

Balancing Chemical Equations (cont. ) • A coefficient in a chemical equation is the number written in front of a reactant or product, describing the lowest whole-number ratio of the amounts of all the reactants and products.

Balancing Chemical Equations • The most fundamental law in chemistry is the law of conservation of mass. This is demonstrated with the balanced equation for the reaction between aluminum and bromine.

Balancing Chemical Equations (cont. )

Section 9. 1 Assessment Which of the following is NOT a chemical reaction? A. a piece of wood burning B. a car rusting C. an ice cube melting into water D. red litmus paper turning blue A. B. C. D. A B C D

Section 9. 1 Assessment What is the coefficient of bromine in the equation 2 Al(s) + 3 Br 2(l) → 2 Al. Br 3(s)? A. 1 B. 2 C. 3 D. 6 A. B. C. D. A B C D

NEW STUFF!!!!!

Types of Chemical Reactions • Chemists classify reactions in order to organize the many types. • There are SIX types that will be covered in this topic. -Decomposition -Synthesis -Combustion -Single Replacement -Double Replacement (Net Ionic Equations) -REDOX

Decomposition Reactions • A decomposition reaction is one in which a single compound breaks down into two or more elements or new compounds. • Decomposition reactions often require an energy source, such as heat, light, or electricity, to occur. • There are 5 types of decomposition rxns

Decomposition Reactions a) carbonates metallic oxide + CO 2 Ca. CO 3 Ca. O + CO 2 b) chlorates metallic chloride + O 2 Na. Cl. O 3 Na. Cl + O 2 c) hydroxides metallic oxide + H 2 O Mg(OH)2 Mg. O + H 2 O d) oxy acids nonmetal oxide + H 2 O H 2 SO 4 SO 3 + H 2 O e) binary compounds 2 elements Na. Cl Na + Cl 2 Rules: -When writing the formula for a new compound YOU NEED TO LOOK AT THE CHARGES ON YOUR ION SHEET AND BALANCE THE COMPOUND -Once the compounds are written, BALANCE IT! -Don’t forget about the Diatomic Elements! (7, 7, 7)

Types of Chemical Reactions • A synthesis reaction is a reaction in which two or more substances react to produce a single product. (Others will call this “composition”) • Synthesis reactions will work in the opposite way of decomposition reactions

Types of Chemical Reactions (cont. ) • In a combustion reaction, oxygen combines with a substance and releases energy in the form of heat and light. • The products of a combustion rxn always have CO 2 and H 2 O. General Form: Cx. Hy + O 2 CO 2 + H 2 O

Replacement Reactions • A reaction in which the atoms of one element replace the atoms of another element in a compound is called a single replacement reaction. A + BX → AX + B

Replacement Reactions (cont. ) • A metal will not always replace a metal because of differing reactivities. • An activity series can be used to predict if reactions will occur. • Higher up = more reactive • Elements from Li to Na can displace hydrogen in water to form a metallic hydroxide and H 2 gas.

Single Replacement Reactions PRACTICE: Na. Cl + F 2 _____ + _____ Fe. Cl 2 + K _____ + _____ HCl + Zn _____ + _____ HCl + Au _____ + _____ H 2 O + Na _____ + _____ H 2 O + Fe _____ + _____ Ag. NO 3 + Cu _____ + _____

Replacement Reactions (cont. ) • Double replacement reactions occur when ions exchange between two compounds. • This figure shows a generic double replacement equation.

Replacement Reactions (cont. ) • The solid product produced during a chemical reaction in a solution is called a precipitate. • All double replacement reactions produce either water, a precipitate, or a gas. If one of the products is not one of these, the reaction does NOT occur. • When predicting products, a solubility chart is used to find precipitates. -(aq) means that it is soluble: no precipitate -(s) means there is a precipitate

Replacement Reactions (cont. ) • This table summarizes different ways to predict the products of a chemical reaction.

Section 9. 2 Assessment Which of the following is NOT one of the types of reactions? A. deconstructive B. synthesis C. single replacement D. double replacement A. B. C. D. A B C D

Section 9. 2 Assessment The following equation is what type of reaction? KCN(aq) + HBr(aq) → KBr(aq) + HCN(g) A. deconstructive B. synthesis C. single replacement D. double replacement A. B. C. D. A B C D

Types of Reactions in Aqueous Solutions • An aqueous solution contains one or more dissolved substances (called solutes) in water. • The solvent is the most plentiful substance in a solution. • Ionic equations that show all of the particles in a solution as they actually exist are called complete ionic equations. 2 Na+(aq) + 2 OH–(aq) + Cu 2+ (aq)+ 2 Cl–(aq) → 2 Na+(aq) + 2 Cl–(aq) + Cu(OH)2(s)

Types of Reactions in Aqueous Solutions (cont. ) • Ions that do not participate in a reaction are called spectator ions and are not usually written in ionic equations. • Formulas that include only the particles that participate in reactions are called net ionic equations. 2 OH–(aq) + Cu 2+(aq) → Cu(OH)2(s)

Writing Net Ionic Equations A “net ionic equation” only shows the ions that were used to make the precipitate. Ex: Ca. Cl 2 (aq) + 2 Ag. NO 3 (aq) Ca(NO 3)2 (aq) + 2 Ag. Cl(s) Ionic Equation Written as Ions Dissolved in Water: ___ (aq) + _____(aq) + ____ (aq) _____ (aq)+____ (s) Cancel out the spectator ions and you are left with the Net Ionic Equation! ____ + _____

Writing Net Ionic Equations Practice Problem: Write the net ionic equation for the following reaction. K 2 CO 3 (aq) + Ba(NO 3)2 (aq) _____ + _____ Net Ionic Equation = ____ + ___________

Electron Transfer and Redox Reactions • An oxidation-reduction reaction, or redox reaction involves the transfer of electrons from one atom to another.

In a synthesis reaction, neutral elements become ions (charged particles) and then form ionic bonds. Complete these synthesis reactions: 2 Na + Cl 2 Mg + Cl 2 2 Na. Cl Mg. Cl 2 (Na+ Cl-) (Mg+2 Cl-) Reactions where electrons are transferred and charges change are called oxidation-reduction reactions. (redox)

To represent the change of a sodium atom into a sodium ion we write: Na Na+ + e. This change is the result of the sodium atom losing an electron. To represent this loss, we write the electron as a separate product in the equation. Oxidation is defined as the loss of electrons. Since the electron must eventually be gained by a different atom, we call this a half-reaction.

To represent the change of a chlorine atom into a chloride ion we write: Cl + e- Cl. This change is the result of the chlorine atom gaining an electron. To represent this gain, we write the electron as a separate reactant in the equation. Reduction is defined as the gain of electrons. Since chlorine exists as a diatomic molecule, the reduction half-reaction for chlorine is actually: Cl 2 + 2 e- 2 Cl-

Here’s a way to remember the names of half-reactions: “LEO the lion says GER” Loss of Electrons is Oxidation Gain of Electrons is Reduction

Trends you already know: Metals generally lose electrons in synthesis reactions. Complete and balance the oxidation half-reactions for these metals. K K+ + e. Al Al+3 + 3 e. Non-metals generally gain electrons in synthesis reactions. Complete and balance the reduction half-reactions for these non-metals. 2 e- + Br 2 2 Br 2 e- + S S-2

For each of the following oxidation-reduction reactions, identify which element is oxidized and which is reduced. Ba + oxidized O 2 reduced F 2 Ba. F 2 reduced + 2 Sr oxidized 2 Sr. O

Science or Fiction The carborane superacid was developed in 2004. It is one million times stronger than sulfuric acid. Although this is the world’s strongest acid, it is not very corrosive. Because the acid has a very weak conjugate base, the acid is not very corrosive. It’s chemical formula is HCHB 11 Cl 11 orange = boron, gray = carbon, green = chlorine, white = hydrogen.

Science or Fiction Tropical rainforests must occur between the Tropic of Cancer Tropical rainforests can occur anywhere on the and Tropic of Capricorn (28 degrees above or below the earth as long as on they never frost andofreceive on equator). They receive average 50 -260 inches rain yearly. The rainforests thatinches occur outside of the tropics average 100 of rain per year. are considered temperate.

Oxidizing and Reducing Agents 2 K(s) + Br 2(g) 2 KBr(s) • K oxidized – K is also called the reducing agent (electron donor). – The reducing agent reduces something else. • Br reduced – Br 2 is also called the oxidizing agent (electron acceptor). – The oxidizing agent oxidizes something else.

In each reaction, identify the atoms that are oxidized and reduced, then label the oxidizing agent and the reducing agent. 1. Na + Cl 2 Na. Cl Oxidized = Na Reduced = Cl 2 Oxidizing Agent = Cl 2 Reducing Agent = Na 2. Mn + S 8 Mn. S Oxidized = Mn Reduced = S 8 Oxidizing Agent = S 8 Reducing Agent = Mn

Voltaic Cells: Simple Batteries The below picture is a voltaic cell using Zinc and Copper • Anode: Oxidation Zn Zn+2 + 2 e • Cathode: Reduction 2 e- + Cu+2 Cu

Cleaning Supplies Cleaning supplies are often oxidizing agents and reducing agents. When mixed, cleaning supplies can make a dangerous gas that will poison your family. DON’T MIX THEM!!!

Balancing Redox Reactions

When balancing redox reactions you must consider the charge as well as the atoms, since the total number of electrons must be conserved in the reaction. Below please break down the following into half-reactions to balance: Zn + Ag+ Zn 2+ + Al. N+ Mg Al + Ag Mg 3 N 2

Section 9. 3 Assessment An equation that includes only the particles that participate in a reaction is called: A. net ionic equation B. spectator ions C. complete ionic equation D. reduced ionic equation A. B. C. D. A B C D

The law of conservation of mass requires what in a chemical reaction equation? A. both sides of the equation to contain the same substances B. the reactants to have the same amount of molecules as the products C. both sides to have the same amount of atoms of each element D. the products to have fewer molecules than the reactants A. B. C. D. A B C D

A reaction that gives off heat is what type of reaction? A. single replacement reaction B. double replacement reaction C. synthesis reaction D. combustion reaction A. B. C. D. A B C D

Ions that are present in a solution and do not participate in a chemical reaction when another substance is added are called ____. A. spectator ions B. reactants C. products D. net ions A. B. C. D. A B C D

A double replacement reaction produces all of the following except ____. A. gases B. solids C. light D. water A. B. C. D. A B C D

What type of reaction is the following? 2 H 2 O(l) + energy → H 2(g) + O 2(g) A. synthesis reaction B. decomposition reaction C. combustion reaction D. replacement reaction A. B. C. D. A B C D

What type of reaction is the following? 2 H 2(g) + O 2(g) → 2 H 2 O(l) A. replacement reaction B. synthesis C. combustion reaction D. double replacement reaction A. B. C. D. A B C D

A precipitate forms in a double replacement reaction only if: A. the reactivities of the compounds differ B. the new compound is denser than water C. the new compound is soluble in water D. the new compound is not soluble in water A. B. C. D. A B C D

A ____ is a statement that uses chemical formulas to show the identities and relative amounts of the substances involved in a chemical reaction. A. word equation B. skeleton equation C. chemical equation D. balanced equation A. B. C. D. A B C D

Predict the type of reaction. Li. Br 2 (aq) + 2 Na. OH (aq) → ____ A. synthesis reaction B. combustion reaction C. single replacement reaction D. double replacement reaction A. B. C. D. A B C D

Which reactions are essentially the opposite of synthesis reactions? A. single-replacement B. decomposition C. combustion D. double-replacement A. B. C. D. A B C D